The prior art hand developer is generally composed of a torsion spring, which is disposed between the two handles of the hand developer and intended to serve as a damping mechanism of the hand developer. Such a prior art hand developing device as described above has inherent shortcomings, which are described explicitly hereinafter.
When two handles of the prior art hand developer are pressed by hand to move in opposite directions, the torsion spring disposed between the two handles is so compressed as to generate a quantity of energy, which is stored in the compressed torsion spring. Upon the release of the handles, the stored energy causes abruptly the compressed torsion spring to restore its original form. Such a restoring process takes place abruptly and forcefully such that the hands holding the two handle are often hit by the handles.
The damping effect provided by the torsion spring of the prior art hand developer is so constant that it is not adjustable. As a result, the prior art hand developer is not suitable for use by all persons regardless of their body sizes.
The damping value of the prior art hand developer can not be increased in a direct proportion to the sum of the training hours that a user of the hand developer has accumulated. As a result, the user has to use another hand developer which affords a relatively greater damping effect.
The torsion spring of the prior art hand developer is vulnerable to the spring fatigue, thereby undermining the service life span of the prior art hand developer.